Traditional Fish Passes

This group include fish passes commonly known as Fish Ladders, with several types available, such as:

- Pool-type fish passes, adequate to small obstacles, like weirs. They are designed to allow upstream migrations, but downstream movements are equally possible. Pool-type fish passes consist of several pools, arranged in series of steps separated by cross walls; the type of pool and weir passes may vary, including pool and traverse passes, vertical slot and orifice passes

- Baffled passes (e.g. Denil Fishway), adequate to small obstacles and fish species with elevated swimming capacity (e.g. salmonids); generally, these passes use a sloping rectangular channel with a series of baffles (plates) to deflect water flow velocities. Baffled passes are relatively simple to implement, but have the disadvantage of only a small number of species being able to surpass them.

- Fish locks, adequate lo large dams, but with constrains to their efficiency. Fish are attracted into the downstream holding pool and translocated to the upstream chamber by rising the water level in the first holding pool.

- Fish lifts, adequate lo large dams; fish are directly trapped downstream of the obstacle, and lifted in a trap together with water, with subsequent release upstream. High mortality may occur if a large number of fish is trapped, and downstream migrations are not possible.